Conventional reciprocating internal combustion engines are very complex mechanisms employing a great many parts which are subject to wear and which contribute to losses in efficiency due to friction. Friction occurs between the piston rings and cylinder walls as well as between members which convert and transfer the reciprocating motion of the pistons to rotary motion of the output shaft. In four stroke engines, the flow of fuel/air mixtures and exhaust gases is controlled by valve members driven by one or more camshafts which add further friction losses. Most modern four stroke engines, such as for automobiles, are liquid cooled which requires that coolant passages be formed in the blocks and heads. Another problem with conventional piston engines is vibrations which result principally from the pulsed nature of the power strokes and the reciprocating motion of the pistons. Despite the complexities, inefficiencies, and other problems of reciprocating piston engines, such engines have been very successful and form the majority of prime movers for ground transportation and many other uses.
Attempts have been made to develop more efficient internal combustion engines which solve the problems inherent in conventional piston engines. For the most part, successes in alternatives to piston engines have occurred in specific areas for certain engines. Gas turbine engines of various types have been applied very successfully to aircraft propulsion, as fairly larges engines, and more recently to military tanks. Wankel type rotary engines have been used successfully in some automobiles and motorcycles, although there were problems initially with excessive wear of rotor apex seals. Wankel engines have reduced vibrations compared to piston engines, and gas turbine engines have greatly reduced vibrations. Additionally, Wankel engines do not require intake and exhaust valves, these functions being controlled by corresponding ports which are effectively opened and closed by the rotor. Thus, Wankel engines have considerably fewer parts than four stroke piston engines.
Many small internal combustion piston engines are of the two stroke type. The principal advantages of two stroke engines are relative simplicity of their design and high power output compared to a four stroke of the same displacement and operating at the same speed. The increased simplicity results from simpler valving requirements. Whereas most four stroke engines employ at least one intake valve and one exhaust valve per cylinder, many two stroke engines employ only one such valve, the other function being controlled by cylinder ports which are opened and closed by the reciprocating piston. The theoretical power increase of two stroke engines results from the development of a power stroke for each revolution of the crankshaft, in contrast to one power stroke for every two crankshaft revolutions in four stroke engines.
The operating cycle of two stroke engines includes a compression stroke and an expansion or power stroke. Exhaust and intake functions occur respectively as the piston approaches and moves away from the bottom dead center position. Intake occurs in overlapping relation to exhaust with the intake cycle preferably beginning and ending respectively after the beginning and end of exhaust cycle. It is difficult to avoid retaining some portions of the exhaust gases within the cylinder after the exhaust function has ended. The relative ability of a two stroke engine to minimize the inclusion of exhaust gases in the fuel/air charge is referred to as the scavenging efficiency of the engine. Because a scavenging efficiency of 100 per cent cannot be realized in practice, the theoretical doubling of the power output of a two stroke engine over a comparable four stroke engine, likewise cannot be achieved.
A class of engines which combines aspects of rotary engines and two stroke engines is rotary vee engines. In a typical rotary vee engine, a pair of cylinder blocks have a plurality of cylinders bored therein in a ring about a cylinder block axis. The cylinder blocks are rotatably mounted with the block axes intersecting at an obtuse angle. Vee shaped double piston assemblies are received in each pair of aligned cylinders in the opposite blocks. The engine may have a drive shaft attached to either or both rotary cylinder blocks. If such a rotary vee engine is oriented with the drive shaft axes in a vertical plane and extending upwardly, as a given piston pair is revolved toward the top of the engine, heads of the pistons approach top dead center (TDC) positions within their respective cylinders. Similarly, as the piston pair is revolved toward the lower side of the engine, the piston heads approach bottom dead center (BDC) positions within their cylinders. Because of the geometry of typical rotary vee engines and because the only degree of freedom for the cylinder blocks is rotation about their axes, the ignition of fuel/air charges within the cylinders causes the cylinder blocks to rotate.
In contrast to the relatively fixed cylinders of conventional piston engines, the cylinders of a rotary vee engine rotate, thereby complicating the supply of fuel and air thereto. In many rotary vee engines, fuel and air are supplied to the piston apex region of the engine and inducted into the cylinders through passages cast into the cylinder blocks. While the casting of internal passages in a metal structure is well established in the metal working industry, it is nevertheless complex and, thus, expensive. The rotary vee engine disclosed in FIG. 6 of U.S. Pat. No. 3,820,208 simplifies the construction of such an engine somewhat by routing air to the cylinders through hollow pistons. However, the supply of fuel to the cylinders in this engine is fairly complex and includes a cam operated fuel injector in each cylinder which receives fuel from a rotary coupling associated with the drive shaft of the engine.
U.S. Pat. No. 3,902,468 discloses a rotary vee engine in which the apex region of the engine is used as a compressor to supercharge the engine. The inner surfaces of the cylinder blocks are disposed at complementary angles to their respective block rotation axes, and the apex portions of each cylinder pair engage inner and outer sealing walls. As the cylinder blocks rotate, the volumes between successive piston sets cyclically expand and contract. A compressible gas or gas mixture is drawn into the volumes as they expand, and the gas is compressed as the volumes contract. Passages are provided in the cylinder blocks to route the compressed gas to the cylinders for ignition and expansion therein to drive the engine.